INTRODUCTION
Acute bronchiolitis is a major cause of morbidity and mortality in young
children associated with steep healthcare costs
worldwide1. The clinical course of bronchiolitis
ranges from mild lower respiratory tract symptoms to severe respiratory
distress from lower airway obstruction. Although there are no
universally accepted criteria to predict disease progression, decisions
regarding further evaluation and management are based on clinical
judgement and the presence of known risk factors2.
Antimicrobial peptides (AMPs), also known as host defence peptides, are
short and generally positively charged oligopeptides expressed in a wide
variety of human tissues. AMPs are secreted into the biofilm covering
the inner surface of the airways and may be involved in the direct
inactivation of viruses. Indeed, recent studies support their antiviral
activity3 and consequently their therapeutic potential
in novel antiviral strategies4 against viruses for
whom no effective treatment is yet available such as
SARS-CoV-25.
Among over one hundred human antimicrobial peptides recognized,
defensins and human cathelicidin are the most extensively studied. Human
cathelicidin is a 18 kDa cationic antimicrobial protein called hCAP-18,
which is encoded by the CAMP gene and is cleaved into two peptide
chains, FALL-39 and LL-37. Recent data show that β-defensin-2 and LL-37
may have in vitro antiviral activity against Respiratory Syncytial Virus
(RSV)6, as well as to other viruses implicated in the
pathogenesis of bronchiolitis7,8. Interestingly, the
exogenous application of LL-37 had protective effect in vivo in murine
models against RSV and Influenza A pulmonary
infections9,10. In addition, recent laboratory studies
have shown that vitamin D plays a vital role in up-regulating the
expression of AMPs in the sight of infection, suppressing inflammation
by modulating cytokine production, and, thereby, reducing the severity
of viral lower respiratory tract infections11,12.
Despite the lack of previous relevant studies, these data suggest that
higher airway mucosal concentrations of AMPs may correlate positively
with serum vitamin D levels and a mild disease course. Therefore, the
aim of this study is to examine the association between the mucosal
production of LL-37 and β-defensin-2 in relation to serum vitamin D
levels and the severity of bronchiolitis.